It is well known in the art to provide a receptacle such as a tray or pan beneath the evaporator coils of an air conditioner to receive water that condenses from the air as it is cooled. A drain pipe is generally connected to a side wall of the tray to drain the condensate water as it accumulates. Because water may stand still in the system, various microorganisms may grow in the tray and drain pipe until they clog up the drainage system. When this occurs, overflowing water may cause considerable damage. Because the drainage system and tray are out of sight and may be relatively inaccessible, they may be neglected until damage occurs. Various methods of applying antimicrobials to the drainage systems have been employed in the prior art. They have not been completely successful in overcoming the problem.